It is well known to provide certain data-intensive systems with large amounts of data memory. In certain situations, this data memory must be highly reliable and tolerate almost any form of fault which could threaten its proper performance. For example, the memory system utilized with a self-contained data-gathering vehicle, such as a submersible for obtaining data from the ocean floor or a spacecraft for obtaining data from an extraterrestrial source, should properly store data in such a manner as to allow retrieval of the data at the end of the mission, even if unexpected occurrences render a portion of the memory unusable. Therefore, it is highly desirable to provide a data memory system which is capable of tolerating faults both in the memory hardware and softward, as well as a memory system in which the performance gracefully degrades even if a high level of faults are present.